1. Field of the Invention
The present invention relates to a sound output device that is used to output sound, and specifically relates to one that is equipped with a multichannel output. The present invention also relates to a method of adjusting sound volume.
2. Description of Related Art
In recent years, the development of multifunctional digital sound has led to a wide use of sound output devices equipped with a multichannel output such as a 5.1-channel output.
As an example of such sound output devices, assume, for example, that there is a 5.1-channel output model on which is written “MAX 100 W/ch” regarding its output. In this case, it is usually understood that the maximum total of outputs of all the channels is 100 W×6=600 W, but the sound output device may not actually have power supply ability that is high enough to drive 5.1 channels simultaneously to their maximum output levels. This tendency is evident particularly in low-cost sound amplifiers.
This is because specifications of such low-cost sound amplifiers are decided and set in view of: the fact that only a small number of actual sound generator sources are configured to fully drive all the channels simultaneously; and achieving low power supply cost. However, in a case of a device whose power supply ability is extremely reduced, if a sound generator source configured such that all the channels are nearly fully driven is reproduced in 5.1 channels with a great volume, the allowable output of the power supply will be exceeded, and the power supply may be destroyed.
For example, assume that the allowable input of the power supply is 100 W, which barely satisfies 100 W/ch. Here, if a 5.1-channel source is fully driven to be reproduced with the maximum volume, the inputted power supply is significantly smaller than 600 W which is required. In this case, various devices forming the power supply are destroyed.
In an effort to overcome the above problem, there has been disclosed and proposed a device where the allowable output of the power supply is small and the power supply is equipped with a constant power control voltage drooping characteristic (a chevron-shaped, or a mouth-turned-down-at-the-two-corners shaped, characteristic) and a device that monitors the output volume (see, for example, Patent Literatures 1 to 3).
[Patent Literature 1] JP-A-2011-23937
[Patent Literature 2] JP-A-2010-45481
[Patent Literature 3] JP-A-2007-53721
However, in the technology used in Patent Literatures listed above, detection/control of electric power and output volume is achieved by using an analog device (for example, a converter or a current detecting circuit). Such a device configuration is prone to be complex.
In particular, in the case where control is performed by using the constant power control voltage drooping characteristic, it is necessary to provide a circuit configuration that detects and feedbacks current increase, which is likely to lead to a cost increase. Furthermore, when indicated in a graph, the current itself continues to increase greatly even in the chevron-shaped portion in the graph, it is necessary to design such that a device on the power supply secondary side has a large allowable current.
Furthermore, in the case of using the constant power control voltage drooping characteristic, in a portion after the chevron-shaped portion, if a sound signal whose load varies in a complicated manner is driven, the linearity of the power-supply voltage is lost, which may invite degradation of the sound quality.